Almost identical to the 6L6 except it has a plate cap. SY has made mention to this tube. Vacuumtubes.com sells them. I bought a quad of them with the adapter bases and they work fine in my Wurlitzer organ amps in place of the standard 6L6GC's.

The adapter bases are needed in order to replace the 6L6 in a socket wired for a 6L6. There are several connections that are different.

I have "smoke tested" a few of these tubes. Beware, most 6BG6 tubes (anything with a coke bottle shape) does indeed have a 19 watt plate rating. They really don't like being pushed beyond this. These do have the same guts as a similar vintage 6L6GB, 807, or 1625 and can usually be substituted for them. The maximum screen voltage rating is 300 to 350 volts (depending on whose data sheet you are reading), which is higher than a 6L6GB of the save vintage (250 to 300 volts). I have cranked them to 400 volts without issue, but watch the plate carefully if you are near 20 watts.

The tubes that VacuumTubes.com sells are from the era where vacuum tube sales were declining and some manufacturers stuffed glass with whatever guts that they had to fulfill contracts. This era produced a few rather strange tubes like 6B4 (a DHT) glass filled with 6AV5 guts (a beam tetrode sweep tube). In this case there are 7027A guts inside an envelope labled 6BG6GA. These tubes are "super 6L6GC's" in a 6BG6 bottle. They can take 35 watts and 450 volts in triode with ease.

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Too much power is almost enough! Turn it up till it explodes - then back up just a little.

My small bench power supply only goes to 400 volts, so that is the upper limit of most of my testing. I ran a bunch of different tubes in SE (triode and UL) at voltages up to 400 volts. I was using fixed bias, so the tubes were seeing the 400 volts less the drop in the OPT. I cranked several 807's and 6BG6G's up and there seemed to be no issue with the voltage, but the plates began to show a dim glow in a dark room at about 20 watts, others showed no color at 24 watts. I get the same results from 6L6GB's from the same era. I would guess that 410 volts is probably OK, but I have not actually gone that high.

If you are using cathode bias, or have a lossy OPT, you are probably not hitting the tubes as hard as you think you are.

I did have one 807 die in a fireworks display, but these tubes were badly mistreated by a previous owner. Almost half of them were physically broken. I am assuming that this one had problems, since it sparked out before I really cranked it up.

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Too much power is almost enough! Turn it up till it explodes - then back up just a little.

I hear yu thanks!
Appreciate all the torture testing you do, saves some of us from doing it.

(Running fixed/adjustable bias with 12ohm cathode resistors)
Yah I got roughly 410-412 on the tube pins them selves, but this is in an amp
that isn't the final one I plan on using these tubes in so I'll tone down the voltage
a bit on the final rig that these will be used in, I do see a very small hint of a rosey
edge on one spot of all the tubes when there run that hot so I think I'm pushin it a bit.

These I'm running right now are RCA, I have a bunch of others that look quite different as
far as the plate structure goes with heavy ceramic looking inserts and strengthening rods that
I am going to run and see if they react about the same way as the RCA version of the 6BG6G do.

I cranked the heck out of the GA's from vacuumtubes.com with no signs what so ever, only tested 4 of the 8.

Quick question regarding this, and old Fender guitar amps.
I see some vintage Fenders used 5881's.
Are 5881's fairly close in specs to a 6L6GB or GC?

Specifically, if I use a pair of these super 6BG6G's in a re-creation of a Bassman, for example (with the correct pinouts & plate caps of course), can these be directly substtutued for the 5881's called for, with the same component values, or should this be optimized?

The schematic shows 432v going to the CT of the OPT, then to the plates,
430v going to the second grid (less a 470 ohm 1 watt resistor's voltage drop from a common point to each one of these grids), and

-48v bias going to a pair of 220k resistors (split to have the result of one of these going to each of the first grids, and there is also a .1/400v cap coming in from each of the plates of the last pre-stage 12AX7 to these points (the triode grid),

and then cathodes of these output tubes directly grounded to B-

I'm working up a parts list, I'd like to keep the output stage original as much as possible, just add mods to the pre-amp stages, not here.
Thanks